The present invention relates generally to electronic amplifying circuits and more particularly to an amplifier responsive to the output of a rate discriminator to provide additional current to an output circuit.
Semiconductor devices operated well within design specifications perform reasonably well for their intended applications, such design specifications being an attempt to optimize certain characteristics of the intrinsic semiconductor material. Some of the more important of these characteristics are current amplification factor alpha (.alpha.), current gain factor beta (.beta.), and the maximum frequency (f.sub.T) at which the device can be operated. In many integrated circuits, the f.sub.T characteristic is replaced by a characteristic called slew rate, which is the maximum rate at which an output terminal can slew from one level to another and is thus related to frequency response. Optimizing one characteristic in the design of a semiconductor device is usually at the expense of degrading the other characteristics. For this reason, many different transistors and integrated circuits are available for different specific applications.
It is sometimes necessary to operate these devices in regions approaching limitations imposed by the inherent characteristics. One such application is the output amplifier sections of an oscilloscope, where high current levels through the output transistors to drive the capacitive deflection plates results in a non-uniform alpha characteristic. This is particularly noticeable in the horizontal amplifier, which amplifies a linear sawtooth voltage to suitably drive the deflection plates at a linear rate to produce a linear time-base sweeping of the cathode-ray tube electron beam. Any current starvation due to changes in alpha at the higher sweep rates, or distortions resulting from f.sub.T or slew-rate limiting results in a non-linear, and therefore unreliable, sweep rate.